1. Field of the Invention
This invention generally relates to apparatus for inspecting or processing sheet materials such as bank notes, and in particular to the stacking or accumulation unit of a sheet material inspecting or processing apparatus. The stacking or accumulation unit includes at least one impeller or stacker wheel to which sheets are selectively fed following inspection or processing, a stepper motor for rotating the stacker wheel in order to accept the sheets and deposit them in a stack, and a stepper motor control circuit for synchronizing movement of the wheel with movement of the sheets by start-stop or intermittent operation of the stepper wheel. Movement of the stacker wheel is timed by the controller so that movement of the wheel occurs solely during the intervals between sheet arrivals, the wheel remaining stationary as individual sheets enter grooves in the wheel so as to prevent collisions between the arriving sheets and edges of the accumulation grooves in the wheel.
The invention also relates to a method of accumulating or stacking sheets following inspection or processing and selective diversion to a stacking or accumulation unit of the type which utilizes an impeller or stacker wheel to collect the sheets and deposit them in a stack. The method involves controlling the stacker wheel so that it moves only during the intervals between arrival of the sheets, and is stationary and perfectly positioned upon arrival of each sheet in order to prevent collisions between the arriving sheets and edges of the accumulation grooves in the wheel.
2. Description of Related Art
In general, the use of stacker wheels, also known as star wheels or accumulation impellers, for the purpose of accumulating and stacking sheet materials such as bank notes following inspection or processing, is well-known. As shown in FIGS. 1-3, the conventional stacker wheel 1 includes a plurality of spiral blades 4 which define accumulation grooves 5. As the wheel is rotated so that the grooves 5 successively are presented to a sheet arrival chute 6, the sheets are selectively diverted into the chute by a pivotal gate 7 based on the results of sheet inspection (for example, based on a determination of banknote denomination). The grooves absorb the forward momentum of the sheets so that they can be stacked without causing damage to the sheets. Following insertion of the sheets into grooves 5, the wheel is operated in a purge mode which deposits the sheets in an accumulation tray or bin 8.
Because of the high speed at which bank notes are processed, damage which can lead to misfeeding or jamming may occur if a sheet collides with one of the spiral blades 4 before properly entering the corresponding groove, as illustrated in FIG. 2. The possibility of collision results from even slight differences in arrival times of the sheets at the entrance to the accumulation device.
To reduce the possibility of collision, it has been proposed to increase the entrance angle so as to decrease the likelihood that a sheet will encounter the trailing side of a blade before entering the groove, but the reduction in collisions that can be achieved is limited. A more effective, but also more difficult solution to the problem of reducing collisions and jamming has been to synchronize rotation of the wheel with detected sheet arrivals by varying the rotation speed of the wheel, and in particular by accelerating or decelerating the wheel to adjust for deviations in arrival times of the sheets at the entrance to the accumulation device.
In order to synchronize rotation of the stacker wheel with arrival of sheets, the conventional apparatus includes, as shown in FIG. 3, at least one optical sensor 9 positioned upstream of the stacker wheel or accumulation unit and arranged to indicate the arrival of the sheet in the entrance chute 6. The optical sensor or sensors have outputs connected to a microcontroller 10. Microcontroller 10 supplies timing signals to a motor controller 11 to enable the motor controller to determine the arrival time of a sheet for the purpose of adjusting the speed that the stacker wheel is rotated by stepper motor 12, so that a sheet will begin entering one of the grooves 5 of the stacker wheel at the exact moment that the groove is aligned with the incoming sheet. In addition, microcontroller 10 synchronizes operation of the gate 7 and/or gate controller 7xe2x80x2 so that notes are properly diverted into the accumulation device or sent downstream to another accumulation device or for further processing.
In the conventional method of controlling the apparatus of FIG. 3, as illustrated in FIG. 4, the motor controller 11, upon being informed by microcontroller 10 of an incoming sheet (step 1), calculates an arrival time for the sheet at the entrance to the groove based on the output of optical sensor 9 (step 2). Based on the detected position or phase of the stepper motor 12, the stepper motor controller 11 then calculates the deceleration or acceleration necessary to cause the groove to be in the proper position at the time of arrival of the sheet (step 3). The process is repeated for the next sheet.
In this method, all speed calculations and adjustments must be carried out between the time of arrival of a sheet at the optical sensor 9 and the time of arrival of the sheet at the stacker wheel 1. In the case of a U.S. or Canadian banknote inspection apparatus, in which individual sheets in the form of banknotes are fed at a rate of 10 sheets per second, the available time between arrival of the leading edge of one of the notes at the optical sensor and entry of the note into the stackerwheel is approximately 13.5 ms, while an additional 22 to 24 ms are required for the trailing edge of the note to enter the groove. Not only does this necessitate rapid processing capabilities, but the high torques required to accelerate or decelerate the motor in the limited time between completion of the speed calculation and arrival of the banknote places great physical demands on the conventional stepper motor used to rotate the stacker wheel.
An example of a prior continuous stacker wheel motor control arrangement which addresses the problem of high torques is disclosed in U.S. Pat. No. 5,641,156. In the system of this patent, in order to reduce the amount of acceleration or deceleration necessary to achieve precise phasing of the stacker wheel and the arriving notes, the stepper motor only accelerates or decelerates the stacker wheel if the pitch, i.e., spacing between notes is outside a predetermined range, and only accelerates or decelerates the note by an amount sufficient to bring the stacker wheel within a predetermined insertion range. In addition, an auxiliary drive is used to accelerate or decelerate the notes themselves in order to further reduce the amount by which the rotation speed of the stacker wheel needs to be varied.
Even with the modifications described in U.S. Pat. No. 5,641,156, however, sophisticated processing capabilities and a relatively high capacity motor are required in order to effect the continuous control necessary to ensure proper phasing, limiting the speed at which notes can be processed, and increasing the cost, weight, and power consumption of the device.
It is accordingly a first objective of the invention to provide a high speed sheet material processing and/or inspection apparatus of the type including a stacker wheel made up of a plurality of spiral blades defining grooves for collecting the sheets following inspection and/or processing, which minimizes the possiblity of jamming due to improperly timed arrival of the sheets.
It is a second objective of the invention to provide a high speed sheet material processing and/or inspection apparatus of the type including a stacker wheel made up of a plurality of spiral blades defining grooves for collecting the sheets following inspection and/or processing, in which successive grooves are perfectly positioned to accept respective successively arriving sheets without the need for continuous control and/or adjustment of the speed of the stacker wheel speed to compensate for variations in arrival times of the sheets.
It is a third objective of the invention to provide a high speed sheet material processing and/or inspection apparatus of the type including a stacker wheel made up of a plurality of spiral blades defining grooves for collecting the sheets following inspection and/or processing, in which successive grooves are perfectly positioned to accept respective successively arriving sheets, and yet which does not require any real-time calculations of sheet arrival time or continuous adjustment of stacker wheel position.
It is a fourth objective of the invention to provide a high speed sheet material processing and/or inspection apparatus of the type including a stacker wheel made up of a plurality of spiral blades defining grooves for collecting the sheets following inspection and/or processing, in which successive grooves are perfectly positioned to accept respective successively arriving sheets, and yet which utilizes a stepper motor arranged to follow a predetermined indexing profile that minimizes required torques in order to reduce required motor capacity while protecting the wheel and sheets captured by the wheel from stresses resulting from sudden repeated acceleration and deceleration.
It is a fifth objective of the invention to provide a high speed sheet material processing and/or inspection apparatus of the type including a stacker wheel made up of a plurality of spiral blades defining grooves for collecting the sheets following inspection and/or processing, which minimizes power consumption of the accumulation device.
It is a sixth objective of the invention to provide a method of controlling a stacker wheel in a high speed sheet inspection and/or processing apparatus, the stacker wheel including a plurality of blades defining spiral grooves, so that sheets arrive at the entrances to the grooves without colliding with edges of the grooves, and yet which does not require real time calculation of arrival times or continuous adjustment of stacker wheel speed to account for variations in arrival times of the sheets at the wheel.
These objectives are accomplished, in accordance with the principles of a preferred embodiment of the invention, by providing a stacker wheel arrangement in which, rather than continuously rotating the stacker wheel and decelerating or accelerating the wheel to adjust the wheel speed in order to cause the grooves to align with the entrance chute at the same time that sheets arrive at the wheel, the stacker wheel is indexed between aligned positions following a predetermined profile and held stationary at the aligned position until the sheet has arrived.
By moving or indexing the stacker wheel between predetermined stationary positions, the invention eliminates the need for real-time calculations of sheet arrival times since the indexing sequence need only be completed at some arbitrary time before the next sheet arrives, and not exactly upon arrival of the sheet at the wheel as in the continuous rotation apparatus and method. Thus, so long as the indexing time is less than the minimum time interval between sheet arrivals, the indexing sequence may be started at any time following insertion of the arrival of a sheet in a groove, and thus may be triggered by any signal associated with sheet arrival, including: (i) signals from an optical sensor situated upstream of the stacker wheel or at the entrance to the accumulation device, (ii) synchronization signals provided by or to a main accumulation unit controller for the purpose of operating the gate, or (iii) the occurrence of any other event associated with sheet arrival. For example, since the time of arrival of a sheet in a groove following detection of the trailing edge of the sheet at the optical sensor positioned before the entrance chute of the conventional stacker arrangement can be predetermined, the indexing procedure can be started a predetermined period after the trailing edge signal from the optical sensor, or the trailing edge of a xe2x80x9csynchxe2x80x9d signal based thereon.
While the manner in which the stacker wheel is indexed may be varied without departing from the scope of the invention, according to an especially preferred embodiment of the invention, the apparatus of the invention includes a PIC microcontroller arranged to generate an acceleration and deceleration profile which advances the stacker wheel a predetermined amount, such as 30 degrees, following entry of a sheet into the stacker wheel. A convenient starting point for the indexing procedure is the falling edge of a synchronization pulse generated by a main controller and sent to the PIC microcontroller, as well as to the gate controller, to indicate that a sheet is arriving and that the sheet is to be diverted to the stacker wheel. The leading edge of the synchronization pulse can occur at any time following the previous pulse, but the trailing edge of the synchronization pulse must occur before the trailing edge of the sheet enters the stacker wheel in order to leave enough time to start of a new synchronization pulse before arrival of another bank note.
By way of example, in the case of U.S. or Canadian banknotes fed at ten notes per second, rotation of the stacker wheel may be set to occur 9.5 ms after detection by the optical sensor of the trailing edge of the bank note, i.e., approximately 4 ms before the trailing edge of the banknote enters the stacker wheel, and thus the indexing process can safely be started by waiting 4 ms following an initial synchronization pulse.
In addition to using the trailing edge of the synchronization pulse to initiate an index cycle, the control apparatus and method of the preferred embodiment of the invention employs the synchronization pulse to determine when to begin a purge cycle, in which accumulated sheets or notes are removed from the stacker wheel. In particular, if there is no synchronization pulse for a predetermined extended period of time, such as 100 ms, a purge cycle of six consecutive indexes is initiated. If a synchronization pulse arrives during the purge cycle, then there must be enough time for the stacker wheel to move to an aligned position and complete at least the current purge index if not the entire purge cycle. Since an index cycle is approximately 30 seconds, so long as the leading edge of the synchronization pulse arrives at least about 35 ms before arrival at the stacker wheel of the banknote or other sheet, there will be sufficient time to complete the purge index.
According to yet another feature of the preferred embodiment of the invention, the stepper motor acceleration and deceleration profile output by the PIC microcontroller to the stepper motor controller may be designed to further minimize forces resulting from sudden acceleration and deceleration of the stacker wheel, by ensuring that the wheel is ramped up to full speed as gradually as possible, and then only gradually decelerated. Further shock protection may be provided by connecting the shaft of the stacker wheel to the motor via a helical spring or other damping device.